The present invention is directed to network communication systems. More specifically, the present invention is directed to a method and system for providing Multi-Protocol Label Switching (MPLS) communications interface or inter-networking point between networks.
In circuit-switched packet networks, such as Frame Relay (FR) and Asynchronous Transfer Mode (ATM), customers request a circuit from the network to carry customer data between two specified end points. A circuit can also be provisioned in an Internet Protocol (IP) network using what is referred to as circuit emulation. Thus, it is understood that packet data routed through a network using ATM, FR or IP technology is associated with a circuit defined by the path between two locations.
Typically, the data packets for a particular circuit may travel a path through a number of different routing devices, such as routers and switches, in a number of different networks to reach their destination. The communication between each routing device is performed over a communication path referred to as a link. When the link is between routing devices in the same network, the trend in present day packet networks is to migrate toward using MPLS protocol to transfer packets over the link. In using MPLS protocol, packet data is transmitted over the link encapsulated with an MPLS label (and sometimes even with a stack of multiple MPLS labels). The MPLS label acts as a data packet header and is used to associate the packet data with a particular circuit and thereby help the routing device properly forward the data packets through the network. As a result, the MPLS labels must be locally unique. That is, on each link, a unique MPLS label must be used to identify each circuit.
When a link is needed between routing devices located in different networks, the traditional way to connect the routing devices is to use a Time Division Multiplexing interface between them and assign circuits to specific time slots on this interface. For example, a circuit could be assigned to the 7th DS1 time slot in a DS3 link used as the interface. The trend, however, in such inter-networking is also to migrate to packet interfaces using the MPLS protocol.
When two routing devices intend to exchange data packets with each other using MPLS, one of the routing devices is selected as the source routing device and the other as the destination routing device. The source device calculates a path to the destination device and then sets up the communication circuit, called a label Switched Path (LSP), along this path. This path may pass through other routing devices and is specified as a sequence of communication links. Typically, on each link in the path, the downstream routing device assigns an MPLS label to the circuit and transmits a message over the link back to the upstream routing device informing it of the selected MPLS label. The upstream routing device can then use the selected MPLS label to encapsulate the packet data for this circuit, and transmit the encapsulated data to the downstream routing device over the link. In many cases the circuits are bi-directional and both routing devices at the two ends of a link act as downstream devices, one in each direction. While the accepted convention is for the downstream device to assign the MPLS label, the procedure is identical if the upstream device assigns the MPLS label. A communications circuit could also span two (or more) networks and could be made up of several circuit segments, one on each network and another between every two networks. There could be source and destination routing devices assigned to each segment of the circuit.
Within a network, the links between the routing devices are established and the routing devices are set up to use a Control protocol (i.e. Routing and Signaling protocol) over these links to set up communications between each other. When the routing devices are located on different networks, however, this is not always the case. Many times, even though the routing devices on different networks are connected by a communications link or inter-networking point there is no available common Control protocol that devices on both networks use to communicate with each other. In some cases this may be due to the fact that the routing devices on different networks are made by different manufacturers. In other cases, this may be due to the different communication technologies, such as ATM and IP, being used by the routing devices on different networks. In any case, the problem is that since there is no available Control protocol the routing devices have no way to assign MPLS labels and communicate the assigned labels to each other.